1.4.2.7 When I use filter or transmit with my .tga image map nothing happens.

POV-Ray can only apply filter or transmit to 8 bit 256 color palleted images. Since most .tga, .png, and .bmp images are 24bit and 16 million colors they do not work with filter or transmit. If you must use filter or transmit with your image maps you must reduce the color depth to a format the supports 256 colors such as the .gif image format.

You might also check the POV-Ray docs on using the alpha channel of .png files if you need specific areas that are transparent.